Multistage pneumatic conveying drying equipment



Jan. 31, 1967 YUJIRO SUGAHARA ET AL 3,300,870

MULTISTAGE PNEUMATIC CONVEYING DRYING EQUIPMENT Filed March 23, 1964 2Sheets-Sheet 1 Jan. 31, 1967 YUJIRO SUGAHARA ET AL 3,300,870

MULTISTAGE PNEUMATIC CONVEYING DRYING EQUIPMENT Filed March 23 1964 2Sheets-Sheece United States Patent O 3,300,870 MULTISTAGE PNEUMATICCONVEYING DRYING EQUIPMENT Yujiro Sugahara, Hiroshi Tsuchida, KiyoshiSato, and

Koichi Usui, Tsuruoka-shi, Yamagata-ken, Japan assignors to MizusawaKagaku Kogyo Kabushlkl Kalsha, Osaka, Japan, a corporation of JapanFiled Mar. 23, 1964, Ser. No. 353,760 3 Claims. (Cl. 3457) The presentinvention relates to improvement in multistage pneumatic conveyingdrying equipment.

There has been well known heretofore a so-called pneumatic conveyingdrying method wherein granules to be dried are dispersed into a hot airstream thereby drying the granules during their movement. There has alsobeen a variety of equipment introduced for this method. In such a knownart, a granule crushing machine of a construction constituting a minimumobstacle to the flow rate was usually disposed in the drying duct forthe-purpose of improving the drying efiiciency by further crushing thewet granules to be dried into a size smaller than that which is justsmall enough to be carried on the hot air. This increases the surfacearea of the granules.

However, such a conventional technique as described above had drawbacks.The finely divided granules tended to be flown away by the exhaust airand therefore collection of such granule-s could not be accomplished tothe satisfactory extent with the use of a known collector such as forexample, a cyclone dust collector. While, for example, a bag filter maybe employed for a better collection, the use thereof not only tends towet the filter cloth but also presents deterioration of the materialwhen a high temperature exhaust air is involved in the process. Moreoverthe use of a bag filter in a large scale operation is not practical. Onthe other hand, application of such collectors, such as a cyclonescrubber or venturi scrubber, to obtain complete collection of finelydivided granule products would not be advantageous because it requiresan additional process for separating water from the products collecteddue to the use of water. In addition, materials of the collectors wouldbe corroded and/or worn off. Furthermore electric collectors are tooexpensive to use from the economical standpoint.

Another defect in the conventional technique results from disposing thecrushing machine in an air stream in which granules to be dried arecarried, because, in such an arrangement, the crushing machine isrequired not to reduce the rate of air stream substantially and as aresult the structural design thereof is obliged to be restricted.Accordingly, when the crushing machine is operated beyond its capacityas seen in most cases, heavy wear of the machine cannot be avoided.

In view of the above, one of the prime objects of the invention is toprovide an improved multistage pneumatic conveying drying equipmentsuitably employed in drying of wet granules.

Another object of the invention is to provide a multistage pneumaticconveying drying equipment for drying wet granules with the least lossof finely divided granule products.

Still another object of the invention is to provide a multistagepneumatic conveying drying equipment for drying wet granules to which acrushing machine of an optional structural design may be adapted with noconcern as to its wear.

Other objects and advantages of this invention will be apparent from thedescription provided hereinafter.

These objects aforementioned may be attained by employing a multistagepneumatic conveying drying equipment for drying wet granules, accordingto the invention, comprising at least two drying ducts including aprelimidispersed into the air current in "ice nary drying duct forpreliminarily drying wet granules and a finishing drying duct forfinishing the drying thereof, a means of feeding the wet granules intothe preliminary drying duct, a means of collecting the preliminarilydried granules delivered from the preliminary drying duct, 21 means offorwarding said collected preliminarily dried granules to a drying ductof the next stage, a means of collecting dried granules delivered fromthe finishing drying duct, a means of blowing hot air into the finishingd-rying duct, a means of sending the hot air discharged from thefinishing drying duct into a pneumatic conveying drying duct of the nextstage and a means of exhausting the air discharged from the preliminarydrying duct. Such equipment is characterized in that a means ofgenerating swirls to cause swirls in the exhausted air current issupplied between the place where the means of sending said exhaust hotair from the air current drying duct, the next stage to the preliminarydrying duct, to said preliminary drying duct is connected with saidpreliminary drying duct and the place where said means of forwarding thewet granules being dried into the preliminary drying duct is connectedwith the preliminary drying duct, thereby dispersing the preliminarilydried granules in the air current. A means of crushing saidpreliminarily dried granules between said means of collecting thepreliminarily dried granules and said means of forwarding thepreliminarily dried granules into the drying duct of the next stage, areprovided.

With reference to the accompanying drawings,

FIG. 1 is the illustrative view of an equipment embodying thisinvention.

FIG. 2 is an enlarged view showing the vicinity of a swirl generatingmeans disposed in a pneumatic conveying drying duct.

FIG. 3 is a plan view of one example of the swirl generating means.

FIlgIC; 4 is a cross-sectional view of the means shown in Hot air from ahot air furnace 1 is divided and blown into a preliminary drying duct 4,an intermediate drying duct 9 and a finishing drying duct 13respectively. Wet fine granules to be dried are fed from a supply vessel2, the preliminary drying duct by means of a rotary swirl generator 3,thereby losing a part of their moisture and concurrently adsorbing finepowders being present in the air stream, passed into cyclone collector 5whereupon being separated from air, and after passing through a rotaryvalve 6, passed into an intermediate drying duct 9 via a chute 7 and agranule crushing machine 8. The granules, after being subjected to thesecondary drying in the drying duct 9 and separated V by the cyclonecollector 10, enter into a finishing drying duct 13 via a rotary valve11 and a chute 12, thereby losing water to a predetermined level andpass through,

a cyclone collector 14 and a rotary valve 15 thereby becoming finishedproducts. On the other hand, hot air exhausted from the cyclonecollector 14 of the finishing drying duct 13 containing dried finepowders is led into the intermediate drying duct 9 by means of an airexhauster 16, wherein it is mixed with the hot air from the hot airfurnace 1, thereby supplementing its heat capacity for the drying. Alsothe fine powders of the products existing in said hot air are caused tocontact with semidried product in the intermediate drying duct 9,whereupOn they are absorbed by said semi-dried products for subsequentcollection. The remaining fine powders which are passed into thepreliminary drying duct 4 via the cyclone collector 10 and an airexhauster 17 being accompanied by the hot air, are caused to contactwith wet granules dispersively suspended above swirls, down stream fromthe swirl generator 3, and are collected essentially as adsorbed by saidwet granules. The thermal energy of the hot air exhausted from theintermediate drying duct 9 and the finishing drying duct 13 isthoroughly utilized at the preliminary drying duct 4, wherein wet coarsegranules are dried, thereby extremely enhancing the thermal efficiencyof the system.

A swirl generating means adapted to the equipment of the invention maybe composed, as shown in FIG. 3 and FIG. 4, of a rotatable axis 31, aplurality of vanes 32 radially fixed around said axis, which generateswirls upon rotation, a member 33 mechanically reinforcing said vanesand a rotation driving means (as not shown in the figures). The swirlgenerating means to be employed in this inven tion, however, is notlimited to that illustrated in the figures but minor modificationsthereof may easily be etfected by those skilled in the industry. Itshould be understood that a swirl generating means of any mechanism maybe employed in the invention providing that the mechanism is capable ofgenerating swirls in an air stream, thereby dispersively suspending wetgranules therein which are supplied into the swirls.

The above swirl generating means must be provided at a place between thespot 18 where a duct through which the hot air exhausted from a dryingduct (such as, for example, the intermediate drying duct the next stageto the preliminary drying duct, is sent to the preliminary drying duct,is connected with the preliminary drying duct and the spot 19 where thesupply pipe 2 for the wet granules is connected with the preliminarydrying duct. While it is essential to provide the swirl generating means3 in the preliminary drying duct 4, it may also be provided in theintermediate drying duct and/or in the finishing drying duct.

The means of dividing preliminarily dried granules must be provided at aplace subjected to no effect of the air stream, that is, a place betweenthe means of collecting the preliminarily died granules and a means ofsupplying said granules to the drying duct of the next stage. Said meansof dividing the preliminarily dried granules may include a roll crusheror others of a suitable structure. A crusher of a suitable structuraldesign and having the desired capacity adaptable to the intended servicemay easily be chosen by one skilled in the art. A crusher may also beprovided in the process in which unfinished product collected from theintermediate drying duct is forwarded to the drying duct at the latterstage, if desired.

Wet granules .which may eificiently be driedwith the use of equipment ofthe invention include those having a diameter larger than about 100p.These can be collected completely by a usual cyclone. Those granuleshaving a diameter small than about 1001!. may preferably be firstprocessed for pellet fiorming before being fed into the preliminarydrying duct. For instance, clays such .as acid clay and kaolincontaining more than about 20% water, activated clay containing morethan about 40% water, gypsum containing more than 10% water, pigmentscontaining more than about 20% Water, resins containing more than 10%water, aluminas containing more than about 40% water, and silicatescontaining more than about 40% water may be dried at a high efficiency,as they are or after being formed into pellets if required, with theequipment of the invention.

When the wet granules supplied to the preliminary drying duct 4 have adiameter larger than about 100p, they may be carried on the exhaust airstream containing fine powders of the product with the aid of a swirlgenerating means, thereby not only recovering the exhaust heat butadsorbing said fine powders in the stream. As a result, the air streamgoing into the collection means 5 contains little of the fine powderyproduct which is hard to collect, hence permitting the use of anordinary cyclone for said collection means 5. The preliminarily driedproduct with the fine powders of the product adsorbed thereon are finelydivided for the first time by a crusher 8 disposed outside the airstream before entering into the drying duct of the next stage. Saidcrusher 8, located outside of the air stream, may be of an optionalstructure and capacity. Additionally, since no vulnerable materials todamage and wear are involved in the path of air stream in the inventionsequipment, a smooth and continuous operation for a long period of timeat a high efiiciency is possible.

Using a three-stage vertical pneumatic conveying drying equipment of thetype as illustrated in FIG. 1, wet activated clay having an averagegrain diameter of about 5 mm. and containing 61% of water was dried upto 12% water content at the rate of 1250 leg. (in dry condition) perhour. The resultant product was crushed by the roll crusher 8 into asize of l nun. or smaller in diameter. The temperature of the hot airfrom the hot air furnace 1 was about 830 C.; the quantity of the fueloil consumed was l./hr.; the total amount of exhaust gas generatedincluding the combustion gas and aqueous vapor evaporated was 9000Nmfi/hr; and the exhaust temperatures at the 1st stage (preliminary),2nd stage (intermediate) and 3rd stage (finishing) were 110 C., C. and300 C. respectively being reduced to a thermal efficiency of about 75%.Further the amounts of water evaporated at each stage were 430 kg./hr.,580 leg/hr. and 560 kg/hr. in order while the moisture contents ofactivated clay processed at the outlet of each stage were 53%, 38% and12% respectively.

The amount of fine powders in the exhaust gas generated during the aboveprocess was calculated in such manner that a portion of the exhaust gaswas passed through a cooler, thereby condensing the gas into a liquid,which was subsequently dried to obtain the fine powders contained in thegas. Thereafter, the fine powder concentration was calculated based onthe weight of the fine powders and the amount of said liquid.

The result showed that the liquid temperature was 565 C., the finepowder concentration was 1.8 =g./l. and the total amount of thecondensed liquid .was 600 l./hr., which represents the total amount ofthe fine powders to be .1.1 leg/hr. This amount constitutes only 0.1% of1250 kg./ hr., the total amount of grains dried.

In the past, when wet granular activated clay containing approximately 61% of water was dried in a rotary kiln the resultant dried productnormally took a form of granules and in this instance, the amount ofpowdery clay flown away reached as much as 5% of the quantity of theclay dried. As seen in the above, a great loss was inevitable, even withthe clay subjected to a prior processing for pellet forming, to reducethe powder flowing away.

The equipment of this invention, however, enables one to produce driedpowdery activated clay in which a loss incurred thereupon is not morethan 0.1% as noted above.

We claim:

1. Multistage pneumatic drying apparatus wherein each stage comprises adrying duct, means for feeding granules to be dried into the dryingduct, means for supplying hot air to the drying duct for drying granulesin the duct whilst carrying them therethrough, and a separator at thedischarge end of the drying duct for separating dried granules from thedrying air, wherein conduits are pro-- vided for leading the air fromthe separator of each stage except the first stage back to the dryingduct of the preceding stage, the air conduit from the separator of thefirst stage leading to exhaust, wherein means are pnovided for feedinggranules discharged from the separator of each stage except the laststage to the drying duct of the next stage, means for crushing partlydried granules being provided at a location between the separator of thefirst stage and the drying duct of the second stage and being free fromthe influence of an air stream, and wherein swirl generating means areprovided for causing swirling of air to be passed through the firstdrying duct, said swirl generating means being positioned in the dryingduct upstream of the means fior feeding wet granules into the firstdrying duct.

2. A multistage peneumatic conveying drying equipment as disclosed inclaim 1 above, in that an average diameter ot the wet grandules is atleast about 100;/..

5 6 3. A multistage pneumatic conveying drying equipment 2,274,789 3/1942 Horesi 3410 X as disclosed in claim 2 above, in that a means ofcollecting 2,406,395 8/ 1946- Noel 3410 the preliminarily dried granulesis a cyclone collector. 2,513,370 7/ 1950 Shaw 3457 References Cited bythe Examiner 5 FREDERICK L. MATTESON, JR., Primary Examiner.

UNITED STATES PATENTS JOHN J. CAMBY, Examiner.

2,068,077 1/1937 Rosin et al 3457 D. A. TAMBURRO, Assistant Examiner.

2,235,683 3/1941 Horesi 34-57

1. MULTISTAGE PNEUMATIC DRYING APPARATUS WHEREIN EACH STAGE COMPRISES A DRYING DUCT, MEANS FOR FEEDING GRANULES TO BE DRIED INTO THE DRYING DUCT, MEANS FOR SUPPLYING HOT AIR TO THE DRYING DUCT FOR DRYING GRANULES IN THE DUCT WHILST CARRYING THEM THERETHROUGH, AND A SEPARATOR AT THE DISCHARGE END OF THE DRYING AIR, WHEREIN CONDUITS ARE PROGRANULES FROM THE DRYING AIR WHEREIN CONDUITS ARE PROVIDED FOR LEADING THE AIR FROM THE SEPARATOR OF EACH STAGE EXCEPT THE FIRST STAGE BACK TO THE DRYING DUCT OF THE PRECEDING STAGE, THE AIR CONDUIT FROM THE SEPARATOR OF THE FIRST STAGE LEADING TO EXHAUST, WHEREIN MEANS ARE PROVIDED FOR FEEDING GRANULES DISCHARGED FROM THE SEPARATOR OF EACH STAGE EXCEPT THE LAST STAGE TO THE DRYING DUCT OF THE NEXT STAGE, MEANS FOR CRUSHING PARTLY DRIED GRANULES BEING PROVIDED AT A LOCATION BETWEEN THE SEPARATOR OF THE FIRST STAGE AND THE DRYING DUCT OF THE SECOND STAGE AND BEING FREE FROM THE INFLUENCE OF AN AIR STREAM, AND WHEREIN SWIRL GENERATING MEANS ARE PROVIDED FOR CAUSING SWIRLING OF AIR TO BE PASSED THROUGH THE FIRST DRYING DUCT, SAID SWIRL GENERATING MEANS BEING POSITIONED IN THE DRYING DUCT UPSTREAM OF THE MEANS FOR FEEDING WET GRANULES INTO THE FIRST DRYING DUCT. 